Thin Gas Layer Research Articles

Ultrasonic Healing of Plastrons.

Superhydrophobic surfaces (SHS) exhibit a pronounced ability to resist wetting. When immersed in water, water does not penetrate between the microstructures of the SHS. Instead, a thin layer of trapped gas remains, i.e., plastron. This fractional wetting is also known as the Cassie-Baxter state (CB). Impairment of superhydrophobicity occurs when water penetrates the plastron and, when complete wetting is achieved, a Wenzel state (W) results. Subsequent recovery back to CB state is one of the main challenges in the field of SHS wetting. Current methods for plastron recovery require complex mechanical or chemical integration, are time-consuming or lack spatial control. Here an on-demand, contact-less approach for performing facile transitions between these wetting states at micrometer length scales is proposed. This is achieved by the use of acoustic radiation force (ARF) produced by high-intensity focused ultrasound (HIFU). Switching from CB to W state takes <100 µs, while the local recovery back to CB state takes <45 s. To the best of authors knowledge, this is the first demonstration of ARF-induced manipulation of the plastron enabling facile two-way controlled switching of wettingstates.

Leidenfrost spheres, projectiles, and model boats: Assessing the drag reduction by superhydrophobic surfaces

Superhydrophobic surfaces are expected to reduce drag on bluff bodies moving in water due to the introduction of a thin air layer around the solid and the resulting partial slip boundary condition. The use of Leidenfrost vapor layers, sustained on the surface of a heated metal body is a reliable method to estimate the maximum drag reduction possible due to such air layers. In the past such an approach was used to estimate the drag reduction on a free-falling heated sphere, in which case the form drag is the lead component of the drag force. Here, we extend this approach to evaluate the effect of the thin gas layers on the hydrodynamic drag of free-falling streamlined projectiles and towed model boats, where the form drag is minimal, and the skin friction drag is the lead component of the drag force. By comparing the drag for streamlined bodies with and without sustained air-layers, we see only incremental drag reductions, for the sub-critical Reynolds number tested herein. The same is true for towed model boats. These results hold both for superhydrophobic surface treatments and Leidenfrost vapor layers. Thus, we concluded that for the investigated range of sub-critical Reynolds numbers, the skin friction drag is less sensitive to the effect of the thin gas layers compared to the form drag. These novel findings have important implications for the practical potential of energy savings using gas layers sustained on superhydrophobic surfaces.

MULTI-OBJECTIVE OPTIMIZATION OF ROTARY ASSISTED ELECTROCHEMICAL ARC DRILLING (R-ECAD) PROCESS USING GRA

Electrochemical Arc Drilling (ECAD) has demonstrated its effectiveness in micro-machining a variety of materials notwithstanding the inherent properties of materials. The increased machining properties of the ECAD method are a result of the inclusion of rotational effect of the working material. Better electrolyte replenishment, effective debris flushing, thin gas layer development, and spark uniformity are all credited with this improvement. Several input factors affect the machining characteristics of ECAD, making it difficult to simultaneously optimize these factors for several objectives. In order to maximise Material Removal Rate (MRR) and minimising Hole Overcut (HOC), this paper focuses on the multi-objective optimization of rotary-assisted ECAD (R-ECAD) input factors. Taguchi's L9 experimental design is used to produce micro-holes, and then Grey Relational Analysis (GRA) is used to perform the multi-objective optimization. The chosen input factors are working material rotation (WR), tool feed rate (FR) and applied voltage (V), whereas the chosen response factors are MRR and HOC. Results indicate that the rotating effect of the working material, which aids in the replenishment of electrolyte and the creation of a stable gas layer surrounding the tool, is notably the most significant input factor. For maximising the MRR and minimising HOC, the GRA-based optimised factors were found to be AIICIIBIII (60 rpm, 40 V, 0.8 mm/min). The responses are greatly improved by 39% as compared to the original machining, as demonstrated by microscopy images obtained during the GRA-based input factor optimization.

Influence of thermal boundary layer on thermophysical properties of construction materials

The paper considers the influence of thermal boundary layer on the thermal conductivity coefficient of building materials. The influence of thermal boundary layer on the thermal characteristics is shown on the example of cellular materials such as foam concrete, gas silicate and vacuum-powder thermal insulation materials.New ideas about regularities and mechanism of action of such factors as pore size, thickness and composition of interstitial partitions on thermal conductivity of porous materials are proposed. The thermal characteristics of porous systems were analyzed using the theory of similarity (calculation of Grasgoff, Rayleigh, and Prandtl criteria). Calculation of these criteria showed that in cellular materials with pore diameter up to 4 mm the convective component does not influence the heat transfer coefficient. The thermal boundary layer, a low-moving thin layer of gas adsorbed on the inner surface of the pore, has a great influence on the heat transfer processes in the pore. The paper considers the structure of the thermal boundary layer from the approach of the electrical surface properties of the pore and the gas in it. It is shown that the structure of the thermal boundary layer depends on the surface charges of the solid phase and gas. In the environment of air or oxygen denser and more homogeneous in structure thermal boundary layer will have materials, which pore walls will have an effective positive charge, and the thermal boundary layer of materials with a large negative surface charge will be loose, inhomogeneous. In hydrogen medium, on the contrary, materials with an effective negative charge will have a denser and more homogeneous thermal boundary layer structure.

Laser-driven hierarchical "gas-needles" for programmable and high-precision proximity transfer printing of microchips.

Micro-transfer printing (μTP) techniques are essential for advanced electronics. However, current contact/noncontact μTP techniques fail to simultaneously achieve high selectivity and transfer accuracy. Here, a laser projection proximity transfer (LaserPPT) technique is presented, which assembles the microchips in an approach-and-release manner, combining high-precision parallelism with individual chip control. An embedded carbon layer with a thin gas layer is generated by an ultraviolet laser, followed by absorbing heat from the infrared laser, to enable the sequential expansion of hierarchical "gas-needles." The level 1 large gas-needle with a substantially growing height can reduce the gap between the microchip and the receiver. Then, the level 2 small gas-needles enable the gentle release of a chip. Therefore, the LaserPPT can obtain a strong adhesion modulation (~1000 times), excellent size scalability (<100 micrometers), and high transfer accuracy of ~4 micrometers. Last, the assembly of a micro-light-emitting diode display demonstrates the capabilities for deterministic assembly of microarrays.

The extremely sharp transition between molecular and ionized gas in the Horsehead nebula

Massive stars can determine the evolution of molecular clouds by eroding and photo-evaporating their surfaces with strong ultraviolet (UV) radiation fields. Moreover, UV radiation is relevant in setting the thermal gas pressure in star-forming clouds, whose influence can extend across various spatial scales, from the rims of molecular clouds to entire star-forming galaxies. Probing the fundamental structure of nearby molecular clouds is therefore crucial to understand how massive stars shape their surrounding medium and how fast molecular clouds are destroyed, specifically at their UV-illuminated edges, where models predict an intermediate zone of neutral atomic gas between the molecular cloud and the surrounding ionized gas whose size is directly related to the exposed physical conditions. We present the highest angular resolution (~0.″5, corresponding to 207 au) and velocity-resolved images of the molecular gas emission in the Horsehead nebula, using CO J = 3–2 and HCO+ J = 4−3 observations with the Atacama Large Millimeter/submillimeter Array (ALMA). We find that CO and HCO+ are present at the edge of the cloud, very close to the ionization (H+/H) and dissociation fronts (H/H2), suggesting a very thin layer of neutral atomic gas (&lt;650 au) and a small amount of CO-dark gas (AV = 0.006–0.26 mag) for stellar UV illumination conditions typical of molecular clouds in the Milky Way. The new ALMA observations reveal a web of molecular gas filaments with an estimated thermal gas pressure of Pth = (2.3 – 4.0) × 106 K cm−3, and the presence of a steep density gradient at the cloud edge that can be well explained by stationary isobaric photo-dissociation region (PDR) models with pressures consistent with our estimations. However, in the H II region and PDR interface, we find Pth,PDR &gt; Pth,H II suggesting the gas is slightly compressed. Therefore, dynamical effects cannot be completely ruled out and even higher angular observations will be needed to unveil their role.

Numerical Simulation and Sensitivity Analysis of Hydraulic Fracturing in Multilayered Thin Tight Sandstone Gas Reservoir

Hydraulic fracturing is a necessary measurement to realize the commercial exploitation of oil and gas, but its application in multilayered thin tight sandstone gas reservoirs is still not perfect, which usually have thin gas layers mixed with complex intervals, and shows a dramatic variation in geological and geomechanical properties in the vertical direction. When conventional hydraulic fracturing methods are applied to this kind of reservoir, it is hard to get proper fracture propagation, especially for fracture height control. Facing this situation, this paper proposes a numerical study of the hydraulic fracturing mechanism and analyzes its influencing factors in the multilayered thin tight sandstone gas reservoir. Relying on a real reservoir in the Ordos Basin in China, relevant geological and geomechanical parameters of major gas layers and interlayers are obtained. According to these parameters, the hydraulic fracturing simulation in the multilayered thin tight gas reservoir model is carried out, based on which, the sensitivity analysis of different geological and fracturing parameters which affect the fracture propagation is performed. Furthermore, a real low-production well after fracturing in this kind of reservoir is selected as an example, and based on the analysis, an optimized fracturing scheme is proposed to adapt to the characteristics of the reservoir. According to the comparison of fracturing and production simulations, the optimized fracturing scheme can prevent hydraulic fractures from breaking through thin interlayers, control the fracture height, and prevent fractures from communicating strata with a high water-bearing layer. At the same time, with the same amount of proppant and fracturing fluid, longer fracture length and better fracture conductivity are created, so that the productivity of the optimized fracture has been greatly improved.

Heat exchange between the fuel element of a nuclear reactor made of uranium oxide and its shell under boundary conditions of the fourth kind

The work is devoted to the heat exchange of a nuclear reactor. Attention was paid to the mathematical modeling of the temperature field of the fuel element and the thin gas layer. It is assumed that the thermal contact between the solid–interlayer system is ideal. Methods of differentiation, integration and approximate methods were used for numerical modeling. The dependence of the thermal conductivity of uranium oxide on temperature was also taken into account. Based on the obtained expression, the linear heat transfer coefficient and linear thermal resistance were also found.

Heat exchange between the fuel element of a nuclear reactor made of plutonium dioxide and its shell under boundary conditions of the fourth kind

The work is devoted to the heat exchange of a nuclear reactor. Attention was paid to the mathematical modeling of the temperature field of the fuel element and the thin gas layer. It is assumed that the thermal contact between the solid–interlayer system is ideal. Methods of differentiation, integration and approximate methods were used for numerical modeling. The dependence of the thermal conductivity of plutonium dioxide on temperature was also taken into account.

Heat exchange between the heat-generating element of the circular section of a nuclear reactor and its shell under boundary conditions of the fourth kind

The work is devoted to the heat exchange of a nuclear reactor. Attention was paid to the mathematical modeling of the temperature field of a heat-generating element of circular cross-section and surrounding it with a thin gas layer. It is assumed that the thermal contact between the solid–interlayer system is ideal. Differentiation and integration methods were used for numerical modeling.

Plane-Parallel Advective Flow in a Horizontal Layer of Incompressible Permeable Fluid

In this paper a new exact solution of the Navier – Stokes equations in the Boussinesq approximation describing advective flow in a horizontal liquid layer with free boundaries, where the vertical velocity component is a constant value, is obtained. The temperature is linear along the boundaries of the layer. Solutions of this kind are used to close three-dimensional equations averaged across the layer in the derivation of two-dimensional models of nonisothermal large-scale flows in a thin layer of liquid or incompressible gas. The properties of advective flow at different values of Reynolds number and Prandtl number are investigated.

Stable solar water splitting with wettable organic-layer-protected silicon photocathodes

Protective layers are essential for Si-based photocathodes to achieve long-term stability. The conventionally used inorganic protective layers, such as TiO2, need to be free of pinholes to isolate Si from corrosive solution, which demands extremely high-quality deposition techniques. On the other hand, organic hydrophobic protective layers suffer from the trade-off between current density and stability. This paper describes the design and fabrication of a discontinuous hybrid organic protective layer with controllable surface wettability. The underlying hydrophobic layer induces the formation of thin gas layers at the discontinuous pores to isolate the electrolyte from Si substrate, while allowing Pt co-catalyst to contact the electrolyte for water splitting. Meanwhile, the surface of this organic layer is modified with hydrophilic hydroxyl groups to facilitate bubble detachment. The optimized photocathode achieves a stable photocurrent of 35 mA/cm2 for over 110 h with no trend of decay.

Equipment for removing moisture when manipulating piece food products

The work presents the scientific basis for the recognition of small specific parts and finished products on a thin gas layer. The proposed principle is based on the use of the interlayer as a carrier and recognizing the main element of the pneumatic system. The purpose of the work is to substantiate the possibility of increasing the production of high-quality piece food production through the introduction of modern automated devices. Together with the design features of the working surfaces of the devices, the creation of universal pneumatic equipment is ensured. The developed equipment is able to successfully solve the problems of moisture removal, sorting, rejection, orientation of the subject of production. The description of the recognition principle is given. The synthesis of elements of the pneumatic system of the type "pneumatic chamber-working surface of the device-thin gas layer-product" showed that they are interconnected. At the stage of synthesis of elements of the pneumatic system and their structural classification, it was possible to unite the characteristic specifics of the described pieces of food industry with the design features of the devices and the operations implemented on them. The presented device schemes have versatility, multifunctionality, ability to manipulate specific pieces, when switching from one standard size of parts to another.

溶融金属液滴の衝突界面における凝固を伴う気孔形成過程の可視化および計測

The rapid cooling single-roll method is widely used to produce amorphous metal ribbons. To obtain more rapid and homogeneous cooling in the method, one needs to prevent the molten metal / solid interface from forming gas pores. We experimentally investigated the pore formation mechanism by directly observing the impact dynamics with the solidification of molten tin drops on a glass and sapphire substrate under an argon gas environment. We also measured the time variation in the temperature distribution on the substrate surface. As a result, we clarified that pores were formed mainly on the poorly conductive substrate, glass. In contrast, on the highly conductive substrate, sapphire, intermittent solidification layers were formed with thin gas layers between them. Furthermore, we derived two characteristic time scales for solidification relating to the sensible and the latent heats by employing one-dimensional thermal conduction analysis.

Amplification Behaviour of Compressional Waves in Unconsolidated Sediments

Similar to horizontal earthquake motions, vertical motions are amplified depedent on the local site conditions which can be critical for the safety of certain structures. Production of natural gas in Groningen, the Netherlands, results in reservoir compaction causing low magnitude, shallow earthquakes which are recorded with a borehole seismic network. These recordings form an excellent data set to understand how shallow unconsolidated subsurface geology influences the amplification behaviour of compressional waves (P-waves). First, we present borehole and single-station techniques (amplification factors, empirical transfer functions (ETF) and V/H spectral ratio implementations) to quantify vertical amplification. We show that vertical-wave incidence is a reasonable assumption. All techniques are capable of emphasising the sites with strong amplification of vertical ground motion during an earthquake. Subsequently, we compare ETF with single-station methods with the aim to develop proxies for vertical site-response using spectral ratios. In a second step, we link vertical site-response with shallow subsurface conditions, like the P-wave velocity and peat content. To better understand the amplification mechanisms, we analytically simulate P-wave propagation. In the simulations, we compute synthetic transfer functions using realistic subsurface conditions and make a comparison with the ETF. The simulations support the hypothesis that thin layers of shallow gas, originating from the Holocene peat, result in wave amplification. We observe strong vertical site-response in particular in the eastern part of Groningen, with industrial facilities and pipeline infrastructure in the region. Here, if high vertical amplifications are persistent at large earthquake magnitudes, appreciable levels of vertical loading may be expected. This study demonstrates that vertical motions should be assessed separately from horizontal motions, given that the amplification behaviour of P-waves is affected by distinctive mechanisms.

Quantum Controller of Gravitational Mass Using Photon Gas

Here, we propose a device that can strongly reduce the Gravitational Mass of a body. Basically, it contains a thin layer of Photon Gas, between the plates of a capacitor, produced by lasers conveniently positioned. By controlling the value of the gravitational mass of the Photon gas, by means of the electric field produced by the capacitor, it is possible to control the Gravitational Mass of a body, when it is placed upon the photon gas. From the technical point of view this device can be used to strongly reduce the gravitational masses of aircrafts or spacecrafts.

Numerical study of hole formation in a thin flapping liquid sheet sheared by a fast gas stream

This study reports aerodynamics effects of a fully developed double-shear layer gas flow in the perforation and disintegration of a thin liquid sheet using three-dimensional numerical simulations. A double-shear layer gas flow, where a thin quiescent gas layer is sandwiched between the two fast moving gas layers, is first simulated up to a statistically steady state. The downstream dynamics of the gas shear layers shows vortex shedding and three-dimensional rib-like vortical structures, similar to the wake of a bluff body. This gas flow is then used as the initial condition for a liquid-gas simulation, where the liquid phase is sandwiched by the top and bottom fast gas streams. A thin liquid sheet with a thickness of 25 μm is considered using air/water conditions. The liquid sheet oscillates and small holes, preceded by craters surrounded by ripples, are formed. The thinning of the liquid sheet, spanwise corrugations, and vortex separations within the liquid-gas boundary layer are shown to govern the dynamics of the liquid sheet. A localized pressure jump is also observed inside the liquid sheet and precedes the rupture of the liquid sheet by pushing the liquid away in the span direction. The holes formed subsequently grow in size, collide and merge with each other, and break the liquid sheet into multiple droplets.

A Study of Fracture Penetration Law of Tight Sandstone Gas Reservoir in Block LX

The fracture of tight sandstone gas reservoir in Block LX is characterized by thick sand body and thin gas layer. The production layer is adjacent to water layer and coal fracture, and the longitudinal stress difference of the shielding layer is small. Based on the theory of fracture tip stress intensity factor, this paper adopts core experiment and theoretical analysis method, combined with fracturing engineering geological characteristics and construction parameters, to analyze the fracture penetration criterion and study the influence of construction factors and reservoir geological characteristics on the law of fracture penetration law. The results show that the minimum horizontal principal stress difference of artificial fracture passing through the interlayer is affected by the construction displacement, reservoir thickness and other factors; The construction displacement has obvious influence on the minimum horizontal principal stress when the artificial fractures pass through the interlayer, and the construction with small displacement can prevent the artificial fractures from passing through the interlayer when the stress difference of the reservoir interlayer is less than 3.5MPa. The minimum horizontal principal stress difference of the reservoir layer when the artificial fracture extends to the interface of he reservoir layer can be determined by using the criterion of the artificial fracture behavior and the model of the artificial fracture behavior, which will provide some technical guidance for the field hydraulic fracturing construction.

Improvement of the design of radial lobe bearing on gas lubrication and development of the corresponding calculation software system

BACKGROUND: With the increase in rotation speeds of turbomachinery shafts, particularly for aviation and space applications due to the requirements for compactness and mass reduction, the issue of bearing life becomes relevant. For such devices, it is promising to use gas lubricated petal bearings (GLPB), which do not require additional systems and operate on the gas of the turbomachine working flow with excellent damping characteristics. Despite the attractiveness of GLPB designs, they are difficult to calculate because the direct work is performed by a thin layer of gas instead of balls, as in classical bearings. The efficiency of a GLPB depends directly on its design, especially the shape of the lobes and the amount of clearance between the shaft and the lobe.&#x0D; AIM: To develop a mathematical model of the operation of a gas lubricated lobe bearing to determine the pressure distribution across the lobe surface and the corresponding computer program for calculations.&#x0D; METHODS: Computational modeling of radial GLPB operation is accomplished with the determination of pressure in the lubrication layer. Moreover, its corresponding integral characteristics within the Reynolds model and the equation for the height of the lubrication layer under several assumptions are determined.&#x0D; RESULTS: In this research, a computer program has been developed that allows for automated calculation of the space of change of variables and functions, the layout of a single table and output, construction of a volumetric model for its subsequent use in CAD systems, and generation of pressure graphs. Herein, the calculation of each variant is faster than similar calculations in the MathCAD environment. The same convenience consists of the block structure of the program, the visual setting of interrelations between blocks, and various and understandable outputs, suitable for both the report (construction of graphs) and drawings and visualization.&#x0D; CONCLUSION: A specialized software package for parametric optimization of gas dynamic characteristics of GLPB has been developed. The developed tool permits the calculation of several cases and facilitates the selection of the optimal gap shape based on numerous proposed criteria. Among other things, the calculation allows us to see the variations in a different operating mode of the plant, use of a different substance with different dimensions, and choose the optimum that will suit a particular plant. Moreover, it is possible to expand the limits of applicability of petal bearings, such as at low speeds or large diameters.

The TW Hya Rosetta Stone Project. III. Resolving the Gaseous Thermal Profile of the Disk

Abstract The thermal structure of protoplanetary disks is a fundamental characteristic of the system that has wide-reaching effects on disk evolution and planet formation. In this study, we constrain the 2D thermal structure of the protoplanetary disk TW Hya structure utilizing images of seven CO lines. This includes new ALMA observations of 12CO J = 2–1 and C18O J = 2–1 as well as archival ALMA observations of 12CO J = 3–2, 13CO J = 3–2 and 6–5, and C18O J = 3–2 and 6–5. Additionally, we reproduce a Herschel observation of the HD J = 1–0 line flux and the spectral energy distribution and utilize a recent quantification of CO radial depletion in TW Hya. These observations were modeled using the thermochemical code RAC2D, and our best-fit model reproduces all spatially resolved CO surface brightness profiles. The resulting thermal profile finds a disk mass of 0.025 M ⊙ and a thin upper layer of gas depleted of small dust with a thickness of ∼1.2% of the corresponding radius. Using our final thermal structure, we find that CO alone is not a viable mass tracer, as its abundance is degenerate with the total H2 surface density. Different mass models can readily match the spatially resolved CO line profiles with disparate abundance assumptions. Mass determination requires additional knowledge, and, in this work, HD provides the additional constraint to derive the gas mass and support the inference of CO depletion in the TW Hya disk. Our final thermal structure confirms the use of HD as a powerful probe of protoplanetary disk mass. Additionally, the method laid out in this paper is an employable strategy for extraction of disk temperatures and masses in the future.